THE MOUTH
The digestive tract is simply all the organs that are instrumental in digestion. It starts with the mouth, which is sometimes called the buccal cavity.
The mouth has three main components: teeth, the tongue and saliva. Teeth are hard structures. The tongue is a muscle. Saliva is the liquid inside the mouth. It is a chemical substance that contains enzymes.
The food we eat starts to be transformed in the mouth. Once it leaves the mouth, food goes into a tube called the oesophagus, which is about 25 centimetres long.
A muscle at the bottom of the throat opens and closes the oesophagus. This muscle is called a sphincter, which either allows or prevents food from passing through.
THE SPHINCTERS
There are several sphincters in the digestive tract. For example, there is another sphincter at the end of the oesophagus to control the entrance to the stomach.
The stomach is a J-shaped muscular pouch that expands when it receives food and drinks. Its average size is 1.3 litres, but a heavy beer drinker’s stomach can reach a volume of 4 litres!
As you may have guessed, there is another sphincter at the bottom of the stomach to regulate the movement of food towards the small intestine. It is called the pylorus.
THE INTESTINES
The small intestine is a narrow, coiled tube that is more than 5 metres long. To put this in context, if stretched out vertically, it would be equivalent to the height of a giraffe!
The small intestine can be separated into three parts: the duodenum, the jejunum and the ileum.
The duodenum is the first part of the small intestine, but since it is closely related to the liver and pancreas, it is often treated separately.
The liver and pancreas are considered accessory digestive glands because, although they play an important role in digestion, food never actually goes through them. It is mainly in the small intestine that nutrients move into the blood to reach the body’s cells.
The last organ in the digestive tract is the large intestine. It is about 1 metre long.
Nutrients first pass through another pouch, located between the small and large intestines.
This pouch is called the cecum. It has a small appendage, called the appendix. The appendix does not participate in digestion, but may become infected. Such an infection is called appendicitis. The large intestine is sometimes also called the colon. Just like the oesophagus and stomach, it also has a sphincter at the end. Most of the time this sphincter is closed, except when stools are evacuated through the anus.
The colon is also divided into three parts: the ascending colon, the transverse colon and the descending colon.
